Technical Paper 13 Embodied energy considerations for existing buildings Gillian F. Menzies September 2011
The views expressed in the research report(s), presented in this Historic Scotland Technical Paper, are those of the researchers, and do not necessarily represent those of Historic Scotland. This paper is available as web publication on the Historic Scotland website: www.historic scotland.gov.uk/technicalpapers This paper should be quoted as: Historic Scotland Technical Paper 13 We welcome comments If you have comments or queries about our Technical Papers or would like to suggest topics for future papers, please do get in touch with us either by email at hs.conservationgroup@scot.gov.uk or by phone on 0131 668 8660. Page i
Embodied energy considerations for existing buildings Contents Introduction Research report by Historic Scotland by Gillian F. Menzies Introduction Historic Scotland Technical Paper 13 forms one of a series of three reports, Technical Papers 12 to 14, that look at some of the wider issues concerning the existing built environment, and how it is altered to respond to current and emerging pressures regarding energy efficiency. These reports comment on topics that are often not fully investigated in the mainstream discussions on energy efficiency and the domestic housing stock. The topics are thermal comfort and energy efficiency (How do we achieve that, and are there ways of making provision for comfort that can do it better than conventional systems?); Indoor air quality and older structures (What is the balance with factors such as ventilation and health?); and finally the topic of this paper, embodied energy (The wider energy costs associated with our choices of materials used in upgrade work, and are they as durable and long lasting as the elements they replaced?) Whole life analysis is important, for modern upgrade cycles are becoming shorter while maintenance cycles are getting longer. We are essentially using components until they break or fail, and then carrying out wholesale replacement of plant equipment or building element. This uses carbon, and reduction in carbon emissions, or their equivalent, is the focus, not reduction in operational energy alone. The present requirements on energy use regulate for the energy efficiency of the building fabric and installed building services, and are calculated based upon standards assertions as to the occupancy and use of the building. The energy, or carbon, expended in the manufacture and installation of energy efficiency elements is not addressed, and thus a situation where the end justifies the means is created. The effectiveness of a low carbon project is judged by its energy in use, not the sum total of the energy expended in its retrofit, nor by the cost of removal and disposal of parts considered to be not sufficiently energy efficient. Such interventions have serious impacts on the fabric of existing traditional and historic buildings where durable elements are replaced with components of shorter life and lower durability. The emerging discipline of embodied energy, or carbon counting, has some way to go if upgrade projects are to be properly evaluated in whole carbon terms. This embodied energy report will seek to develop basic arguments on an approach to this topic where whole life carbon costing should be looked at in addition to energy performance alone. Some of the themes in this series of papers overlap, and this is deliberate, for in discussion of upgrade options many factors come into play, and in complex systems boundaries are sometimes fluid. The views expressed in these reports are those of the authors, and not necessarily those of Historic Scotland or the Scottish Government. Page ii
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Research report Research report Embodied energy considerations for existing buildings Dr. Gillian F. Menzies Heriot Watt University September 2011 Page 1
About the author Dr. Gillian F. Menzies BEng PhD CEng Cenv MIE MHEAH Dr. Gillian Menzies is Lecturer at the School of Built Environment, Heriot Watt University, Edinburgh. In the post since 2000, she has a track record of research in life cycle assessment and sustainable building design. Since 2011, she is also Programme Leader of the university s MSc Carbon Management in the Built Environment. She is a Chartered Engineer, Chartered Environmentalist, CIBSE Low Carbon Consultant, and a member of the Energy Institute. Dr. Menzies holds a BEng Hons (1 st Class) engineering degree from Napier University, Edinburgh, a PG Diploma in Technology Management from the University of Stirling, and a PhD in Environmental Engineering (LCA) from Napier University. She has commercial experience of computerised building simulations, energy analysis, building user comfort assessment, and indoor environment and facilities management. She is the author of one of three reports published as Historic Scotland Technical Paper 9, Slim profile Double Glazing: Thermal Performance And Embodied Energy, published in 2010. Page 2
Contents Executive summary...5 1. Introduction...6 2. Life cycle assessment (LCA) and embodied energy and carbon...7 2.1 Energy and carbon...7 2.2 What is LCA?...8 2.3 What is embodied energy and carbon?...11 2.4 Why does embodied energy and carbon matter?...12 2.5 What impacts on embodied energy and carbon?...14 3. LCA methodologies...16 3.1 Process analysis...17 3.2 Input output analysis...17 3.3 Hybrid analyses...18 3.4 Simplistic / alternative approaches...18 3.5 Which LCA methodology should be use?...19 4. Importance on LCA base data...19 4.1 Databases and inventories...19 4.2 Boundary definitions...21 4.3 Completeness of study...21 4.4 Energy supply assumptions...21 4.5 Energy source assumptions...22 4.6 Product specification...22 4.7 Manufacturing differences...22 4.8 Complications in economic activities...22 5. Current and future use of LCA...23 5.1 Current use of LCA...23 5.2 Future potential for LCA use...24 6. Existing buildings and embodied energy and carbon...26 6.1 Why does sunk energy and carbon not matter?...26 6.2 Building operation...27 6.3 Building maintenance and refurbishment...27 6.4 Building replacement...32 6.5 Considerations beyond energy and carbon...33 7. Conclusions...34 Glossary...36 References...39 Page 3
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Executive summary This report outlines the importance of life cycle analysis (LCA) in assessing the sustainability of new buildings and of maintaining, refurbishing and replacing existing buildings. Embodied energy and carbon is only one part of a building s life cycle, but is of increasing significance. The embodied energy and carbon, associated with building construction, is the energy required and carbon emitted to construct a building (including extraction of raw materials, manufacture of building products and construction of the building.) The other stages of a building s full life cycle are operational energy and carbon (relating to the use of a building) and end of life energy and carbon (relating to its demolition and disposal). This report, intending to support a discussion about energy and carbon assessment of existing buildings, provides an introduction to life cycle thinking generally, before presenting considerations specifically for existing buildings. The report demonstrates that, although embodied energy and carbon is important generally, the energy used and carbon emitted in the past, i.e. the sunk embodied energy and carbon, does not matter in achieving the set UK reduction targets for greenhouse gas emissions. Sunk energy and carbon is of no relevance for mitigating the energy consumption and carbon emissions of today and the future. Nevertheless, there is a strong argument for retaining existing buildings even if their embodied energy and carbon is of no relevance today. The use of durable, long lasting materials as used in many older existing buildings can reduce refurbishment cycles, therefore requiring less energy and carbon long term. However, existing buildings need to be affordable to occupy and maintain, and energy efficiency upgrades might be needed to achieve this. A LCA is required to choose the best long term upgrade solutions. For this, the building s construction type must be taken into account, as some upgrade options might be unsuitable for use in traditional buildings. There will be an argument for replacing some existing buildings with new ones. However, this decision should not be taken lightly. A full LCA should be conducted for the replacement building and should include the end of life energy and carbon of the existing structure. Decisions for energy efficiency upgrades of existing buildings should be made on grounds of energy, carbon and financial costs, but other factors need to be considered, too. Historic buildings, for example, have a cultural and educational value, due to they can play a strong role in creating identity and have a significant economic impact for regeneration and tourism. The sustainable use of existing buildings must be a national and global priority. Replacing a building has significant energy, carbon and financial cost implications. The retention of the existing building stock is, therefore, preferred, where its energy performance is good or can be improved to appropriate levels. Retaining existing buildings and seeking to enhance their energy performance in sensitive ways is in keeping with building conservation, sustainability and progress towards a low carbon society. Page 5
1. Introduction The Scottish and UK parliaments have introduced legislation to cut greenhouse gas emissions that cause climate change. The Climate Change (Scotland) Act 2009 sets out two major targets for reduction of these emissions: 42% reduction by 2020, and 80% reduction by 2050. The current UK commitment is 34% and 80% by 2020 and 2050 respectively (Department Of Energy And Climate Change, 2011). Carbon dioxide (CO 2 ) is a significant greenhouse gas and, consequently, these emission reduction targets apply to CO 2 emission, often simply referred to as carbon emissions. These emissions are inextricably linked to energy consumption, when energy is produced through the combustion of fuels. Buildings require large quantities of energy for operation: around 40% of UK energy is used in buildings. The construction industry is also, globally, the highest consumer of materials, using around 6 tonnes of material per person per year. It is, therefore, not surprising that, relating to energy use in and carbon emissions from buildings, a number of policies, directives, regulations, guides and incentives have been generated, or substantially amended, over the last ten years, such as the Energy White Paper (Department of Trade and Industry, 2007), the Energy Performance of Buildings Directive (European Union, 2002), Section 6: Energy of the Scottish building standards (Scottish Government, 2011) and Part L: Conservation of Fuel and Power of the building regulations for England and Wales (HM Government, 2010), the introduction of Energy Performance Certificates (and in England and Wales Display Energy Certificates), the Carbon Reduction Commitment, Carbon Trading, and Climate Change Levies. The construction industry has become proficient at designing and erecting low energy buildings within a relatively short time period (mid 1990s to date). Coupled with this is a growing understanding by the general public of the need to conserve energy both for security of future supply and to protect the environment. In times of critical financial uncertainty, the general public is acutely aware of energy costs and is particularly eager to cut fuel bills. The 2010 BP Statistical Review of World Energy (BP plc, 2010) revealed a decline in the amount of energy used throughout the recent recession; the first decline since 1982. Unsurprisingly, given all these recent developments, the assessment of energy use and carbon emissions related to the construction of buildings and their operation has developed significantly over the past decades. However, this development has, to date, focused on operational energy, i.e. the energy related to the use of a building. Embodied energy, i.e. the energy related to the construction of a building, has been somewhat neglected. (The same applies to end of life energy, i.e. the energy related to the demolition and disposal of a building.) There are a wide number of technologies, software programs, tools and initiatives now in use to help reduce operational energy and carbon, but the practical application of methods to assess and reduce the embodied energy and carbon of building construction is still in relative infancy. Page 6
Energy and carbon assessment in the construction industry has also focused much on the construction of new buildings. Assessing the energy and carbon related to existing buildings was all too often limited to only operational energy. The energy and carbon associated with the maintenance and repair, upgrade and refurbishment, and demolition and replacement of existing buildings is not that often assessed properly, if at all. This report highlights the importance of embodied energy and carbon related to building construction and intends to support a discussion about the energy and carbon assessments of existing buildings. Aimed at practitioners in the building professions and construction industry, the report provides an introduction to state of the art life cycle thinking generally (Sections 2 to 5), before presenting considerations specifically for existing buildings (Section 6) and conclusions (Section 7). Section 2 introduces embodied energy and carbon, including the underlying concept of life cycle assessment (LCA); Section 3 briefly outlines the currently used LCA methodologies; Section 4 highlights the importance of the base data used in LCA; and Section 5 describes how LCA is currently being applied and how it might develop in the future. Whereas sections 2 to 5 discuss LCA generally, Section 6 focuses on existing buildings: It discusses why the sunk embodied energy and carbon of existing building i.e. energy and carbon spent in the past is of no relevance in achieving the set emission reduction targets; it highlights why, despite this irrelevance, existing buildings do play a major role in achieving emission reductions, through well considered maintenance and repair, and upgrade and refurbishment; and it argues that, when deciding about building replacements, the demolition of existing buildings needs to be properly assessed and considered. Section 6 also briefly considers two particular types of existing buildings: historic and traditional buildings. Section 7 summarises the considerations outlined in this report. 2. Life cycle assessment (LCA) and embodied energy and carbon The embodied energy and carbon of a building are one part of the overall energy and carbon of the building, measured over its complete life (life cycle). So it is important, firstly, to introduce the terms energy and carbon, and then describe the concept of life cycles and their assessment, before discussing in more detail embodied energy and carbon, and, finally, what impacts on them. 2.1 Energy and carbon Energy is needed to construct and operate a building. This energy is often produced through the combustion of fossil fuels, such as coal, gas and oil. The combustion process generates the energy used, for example, in the construction and operations of a building. However, this process also produces, as by products, CO 2 and other gases, emitted into the atmosphere. It is these CO 2 emissions which are, generally, referred to in shortened form as carbon. In other words, energy, generally measured in joules (J) or mega joules (MJ), is converted into carbon, measured in kilograms (kg) or tonnes (t). Energy consumption is, Page 7
therefore, inextricably linked to carbon emissions, when (fossil) fuels are used. However, other forms of energy exist, for example, solar energy (a form of radiant energy) or wind energy (a form of kinetic energy), which do not generate carbon emissions when converted. Physically, energy is neither consumed nor produced, but converted from one form of energy into another. Energy can be in the form of, by example, thermal energy (heat), electrical energy (electricity) and kinetic energy (movement). CO 2 is only one of several greenhouse gases impacting on climate change through global warming. Instead of using CO 2 only, when assessing global warming, equivalent carbon dioxide (CO 2 e) is frequently used as a measure. This is a way of describing how much global warming a given type and amount of greenhouse gas may cause, using the functionally equivalent amount, or concentration, of CO 2. Put simply, if CO 2 has a global warming potential (GWP) of 1, then methane has a GWP of 25 and nitrous oxide a GWP of 298. It is important not to confuse the term carbon, as generally used in this report, with the chemical element of the same name. Carbon, in the context of this report, refers to CO 2 emissions. However, the word carbon can also refer to the chemical element carbon (chemical symbol C), which occurs as element in form of graphite, diamond or amorphous carbon (the element s free, reactive form), or as a compound in, by example, CO 2, carbonate rock (e.g. limestone, dolomite and marble) and hydrocarbons (e.g. coal, petroleum and natural gas). Plants can absorb CO 2 from the air, storing the carbon element in form of carbohydrates (sugar). This storing of carbon is referred to as carbon sequestration or carbon capture. That means that chemical carbon can be contained, as a chemical compound, in materials which are used in building construction, e.g. building stones and timber. However, this storage of carbon in a (raw) material does not relate to the CO 2 emissions released in the process of making a building product out of the (raw) material. So, when in this report the term carbon is used, it refers to CO 2 emissions and not to the chemical element. 2.2 What is LCA? To create a building, energy is needed for the extraction of raw materials, the manufacture of building products and the construction of the building on site. Energy is also needed to operate a building in use, e.g. for heating, lighting, cooking and working. And energy is needed at the end of the life of a building for its demolition and disposal. Figure 1 illustrates the various life cycle stages of a building. If a boundary is drawn around this life cycle of a building, an assessment of the inputs and outputs which cross this boundary can be made. Such an assessment is called life cycle assessment or life cycle analysis (LCA). It includes the entire life cycle of a product, process or system: encompassing the extraction and processing of raw materials; manufacturing, transportation and distribution; and use, reuse, maintenance, recycling and final disposal (Consoli et al., 1993). The execution of a LCA relies heavily on data generally provided in life cycle inventory (LCI) databases. (LCIs are discussed in more detail in Section 4.1.) Page 8
Figure 1 Life cycle stages of a building with associated inputs and outputs LCA can be used as an accounting methodology to quantify energy use and carbon emissions for the whole life cycle of a building. In this context, LCA often utilises accountancy speak: energy and carbon can, for example, be expended, invested or spent. LCA is a much explored concept and has been used as an environmental management tool worldwide since the late 1960s. It is an internationally recognised tool for assessing the environmental impact of products, processes and activities, using environmental impact indicators. LCA based, for example, on the BRE s Environmental Profiles methodology (BRE, 2011) identifies 13 environmental impact indicators, as listed in Table 1. It is worth noting that climate change (or global warming) is only one of them and accounts for just less than 25% of the impacts. Life cycle energy analysis (LCEA) emerged in the late 1970s and focuses on energy as the only measure of environmental impact of buildings or products. The purpose of LCEA is to present a more detailed analysis of energy attributable to products, systems or buildings. It is not developed to replace LCA, but to compare and evaluate the initial (capital, embodied) and recurrent (operational) energy in materials and components. End of life (EoL) issues should also be considered, i.e. the energy required to recycle and reprocess materials, or to dispose of them safely. LCEA is often used to estimate the energy use and savings over a product or building life, and to compare energy payback periods. Page 9
Table 1 LCA environmental impacts (Anderson et al., 2009) Climate Change Water extraction Mineral resource extraction Stratospheric ozone depletion Human toxicity Ecotoxicity to fresh water Nuclear waste Ecotoxicity to land Waste disposal Fossil fuel depletion Eutrophication Photochemical ozone creation Acidification Life cycle carbon assessment (LCCA) is likened to LCEA and relies on prevailing energy structures to convert mega joules (MJ) of energy to kilograms (kg), or tonnes (t), of CO 2. Life cycle assessments can be carried out for a full life cycle, from extraction of raw materials to disposal or recycling of the end product after use. However, often life cycle assessments are only carried out for parts of the full life cycle. Such commonly used assessment variants are shown in Table 2. Table 2 Life cycle variants commonly used in LCA Cradle to Gate Cradle to Site Cradle to Grave Cradle to Cradle describes the impacts associated with products, materials or processes up to the point at which they are packaged and ready for delivery to site. describes the impacts associated with suppliers (raw materials), transportation to manufacturing centre, manufacturing, packaging and transportation to site. In the case of construction impacts, this would also include any processing required on site to make use of the product or component. describes all the processes which a product or component goes through from raw material extraction to obsolescence and final disposal. It assumes no end of life residual value. is similar to Cradle to Grave, but assumes that an obsolete building, product or component has a residual value at the end of its first life. It assumes that construction waste can be recycled and used to provide raw materials for the re manufacture of the same product or the manufacture of a new and different products. Page 10
2.3 What is embodied energy and carbon? Generally speaking, a building product (i.e. construction material, product or component) has three main stages to its Cradle to Cradle energy life cycle: embodied energy, operational energy and end of life energy. Embodied energy is the energy related to the construction of a building; operational energy is associated with the use of a building; and end of life energy is related to the disposal or recycling of a building. The sum of embodied, operational and end of life energy is referred to as overall energy or total energy footprint. Carbon is a conversion of energy from mega joules to kilograms of CO 2. Consequently, embodied carbon relates to the construction of a building, operational carbon to its use, and end of life carbon to its disposal or recycles. The sum of all three is the overall carbon or total carbon footprint. In other words, embodied carbon can also be defined in relation to life cycle variants as a Cradle to Gate or Cradle to Site analysis (see Table 2), based on energy inputs only (i.e. those energy inputs relating to raw material extraction, transportation, processing, manufacturing and packaging). Product manufacturers may give embodied energy figures for their products which take into account only some of these stages. The definition of the boundaries of a LCA is critical in drawing useful conclusions on the embodied energy of a product. In general, the more manufacturing processes a product undergoes the higher its embodied energy will be. For example, laminated timber products have a significantly higher embodied energy than the equivalent dimensions of sawn timber, as illustrated in Table 3. Table 3 Embodied energy and carbon of selected timber products (Cradle to Gate variant) (Hammond et al., 2011) Material Embodied energy MJ/kg Embodied carbon kg CO 2 e / kg High density fibreboard 16.0 0.58 Glued laminated timber 12.0 0.45 Plywood 15.0 0.65 Sawn softwood 7.4 0.39 Energy and carbon has been spent in the past, is being spend now and will be spent in the future. If spent in the past, this is referred to as sunk energy and carbon. A building which is planned, but not yet built, has no sunk energy and carbon. When built and ready to be used, the building has sunk embodied energy and carbon, but not yet any operational energy and carbon. A building at the end of its life, but not yet demolished, has sunk embodied and operational energy and carbon. The relevance of sunk embodied energy and carbon, when assessing existing buildings, is discussed in more detail in Section 6.1 below. Page 11
2.4 Why does embodied energy and carbon matter? The embodied energy of a building is generally important, because it is an integral and unavoidable part of constructing buildings for use by their occupants. The significance of embodied energy within LCEA has also increased, due to higher energy efficiency levels during a building s operational life and improvements in LCEA methodologies, as will be illustrated in more detail below. (However, although embodied energy and carbon is generally important, Section 6.1 will discuss why sunk embodied energy and carbon does not matter for mitigating the energy use and carbon emissions of today and the future.) It is possible that measures to reduce the operational energy of buildings will result in an increase of embodied energy: using additional embodied energy, for example through the responsible selection of building products, may significantly reduce operational energy and overall energy. This can be illustrated with the following example: To improve the thermal performance of external walls, the thickness of the insulation layer could be increased. Using more insulation means that more embodied energy and carbon is needed. The improved thermal performance of the wall will result in a reduction of the operational energy. So, in this example, an increase in embodied energy resulted in a reduction of operational energy. As the energy life cycle is made up of embodied energy plus operational energy plus end oflife energy, a decrease in operational energy can result in an increase in embodied energy in percentage terms (i.e. the ratio of embodied to operation energy). A building s operational energy obviously depends on its life time, whereas embodied energy and end of life energy are, generally, independent of this. The longer the building s life time the more significant the operational energy becomes in comparison to the embodied energy and end of life energy. Therefore, an increased embodied energy can be justified (recouped / paid back) through savings in operational energy over the life time of the building, if the life time assumed is long enough. This is illustrated in Figure 2 and Figure 3. Building design decisions, other than insulation, which can increase the embodied energy, but reduced the operational energy, can include thermal mass of a building (which helps to control temperature changes within a building), solar gain (through choice of glazing and shading devices) and building form and finishes. (Expanding on these important issues is, unfortunately, outside the scope of this report.) In 1991, BRE estimated that, for a then typical 3 bed detached house, the operational energy would overtake the embodied energy of materials and construction in a period of two to five years (Department of Communities and Local Government [CLG], 2006, p.3). Assuming the house had a life of 60 years before requiring major refurbishment, the energy in use would exceed the embodied energy by 12 to 30 times. Embodied energy was estimated to account for approximately 10% of total life cycle energy (total energy footprint) over a 60 year period. Within two decades this percentage has changed markedly and subject to current and future building regulations will continue to shift. For new, well insulated, energy efficient buildings, embodied energy can account for 40 to 60% of the total energy footprint and can even exceed the operational energy use (Dixit et al., 2010). Page 12
EoLE Building with, say, 100mm insulation, resulting in lower EE but higher OE Building with 200mm insulation, resulting in higher EE but lower OE Figure 2 Comparison of total energy of two buildings with different embodied energy values resulting in different operation energy values: over the same building lifetime, the building with a higher embodied energy, but a lower operational energy can have a lower total energy. (EE = Embodied energy; OE = operational energy; and EoLE = end of life energy) Figure 3 Comparison of life cycle energy of two buildings (with end of life energy not considered): Building 1 has less insulation and therefore less embodied energy (EE1) but more operational energy (OE1) (per time unit) than building 2, which has more insulation and therefore more embodied energy (EE1) but less operational energy (EE2). Page 13
The importance of embodied energy can also be dependent upon the building type and the use to which it is put. For example, distribution warehouses do not consume large amounts of energy for heating and lighting (low operational energy), which means that the embodied carbon component within the building lifecycle is comparatively high. Sturgis Associates, calculated, for example, that the embodied carbon in a distribution warehouse is 60% of its total (life time) carbon footprint; a supermarket, which is energy intensive (high operational energy), has an embodied carbon content of 20%; whereas a house has approximately 30% (Lane, 2010). This draws out an important argument in favour of absolute embodied energy values, rather than percentage of life cycle energy terms: it is possible that two buildings could have the same percentage of embodied to operational energy, yet have vastly different absolute values. An argument can perhaps be made for varying benchmarks based upon building use and type. It certainly supports an argument for considering LCA techniques in building design, renovation and upgrade works. The closer we progress towards the ambition of zero carbon buildings, the bigger the percentage that embodied carbon contributes to the total carbon footprint. Therefore, by the end of 2019 embodied carbon will make up 100% of a building s footprint (in theory). If the determination is to make all buildings zero carbon within the next eight years, embodied energy must be recognized for its importance. Designing buildings to emit no net CO 2 on an annual basis without due regard for the embodied carbon will not satisfy the intended progress towards the 2020 and 2050 emission reduction targets. 2.5 What impacts on embodied energy and carbon? The embodied energy of a building, as has already been pointed out, is the energy and carbon spent for raw material extraction, manufacturing of building materials and construction of the building itself including the energy and carbon spent on the transport associated with these activities. It, therefore, becomes clear that the quantity and type of energy used in these activities is of importance. In the following, three aspects impacting on embodied energy and carbon will be described in more detail: the opportunities for the use of recycled materials, the relevance of the carbon intensity of the energy used, and the importance of low carbon supply chains. Use of recycled materials To make any product, energy is, first of all, needed for the extraction of the raw materials the product is made from. That means that, if a product is made from existing materials, no raw materials are needed and the associated energy is saved. This can be illustrated with the energy needed to produce an aluminium window. Aluminium is generally associated with a very high embodied energy. However, as Table 4 below shows, if made from 33% recycled material, a reduction of embodied energy and carbon of approx. 86% can be achieved. Similarly, manufacturing steel from 39% recycled material reduces the energy and carbon required; however, because virgin steel has a much lower embodied energy and carbon compared to aluminium, the associated energy and carbon saving is also less, approx. 30%. Page 14
Table 4 Embodied energy and carbon of virgin and partly recycled aluminium and steel (data from ICE database; see Section 4.1 and also compare to Table 6) Material Aluminium (100% virgin) Aluminium (33% recycled) Steel (100% virgin) Steel (39% recycled) Embodied energy MJ / kg 218 29 35.4 25.3 Embodied carbon kg CO 2 e / kg 12.79 1.81 2.89 1.95 Carbon intensity of energy supplies How energy is generated has an immense impact on the quantity of carbon emission associated with its generation. Energy generated from fossil fuels generally produces more carbon emissions than biomass. When generated with solar, wind or hydro power, there is no carbon emissions associated with the energy. This means that, using again the example of the aluminium window, such a window would have a significantly lower embodied carbon if produced, e.g., with hydroelectric power. Unfortunately, it is often not easily established from data, such as that provided in Table 4, what forms of energy have been taken into account when converting energy into carbon. The way how energy in the form of heat and electricity is generated is changing, too. The 20:20:20 initiative aims to generate 20% of EU s electricity from renewable sources by 2020, i.e. it is aiming to de carbonise electricity. In current calculations, embodied energy and carbon can be treated somewhat similarly, when used as sustainability indicators. However, as the carbon intensity of electricity and heat distribution reduces, the emphasis of focus will change to embodied carbon, rather than energy. Finding more sustainable ways to generate electricity and heat energy is essential to maintaining economic and social sustainability. The ultimate aim is, of course, to contribute to achieving the set 2020/2050 emission reduction targets. However, embodied energy is important, too. Supplying reliable and green energy is costly in terms of infrastructure, maintenance and distribution. Conserving low carbon energy is, therefore, critical to a low carbon society. Low carbon supply chains A low embodied energy product can have its green credentials negated, if it has to travel long distances to its processing centres and to the construction site. For example, a concrete block sourced from a factory in the locality, or a building stone from a quarry near the construction site, will contain less embodied carbon than one from China, because of the energy used to transport it. Different modes of transport have varying CO 2 emissions. Table 5 details average carbon emissions of various means of transport. Table 5 Transportation embodied carbon (Hutchins UK Building Blackbook, 2010) Means of transport Road Rail Shipping Average CO 2 emissions (kg / t km) 0.32 0.04 0.01 Page 15
Another example, showing how the effects of a low U value component can be negated by transportation and logistics, is that of a novel double glazing unit produced in Japan: the unit, manufactured using vacuum technology in place of inert gas infill, has its naturally low embodied energy and carbon cancelled, if the product is transported by air from Japan instead of using container shipping (Menzies, 2010). Ensuring that procurement allows, in this case, for slower means of transport can significantly lower the associated embodied energy and carbon. The World Economic Forum identified five opportunities for users of logistics and transport services to decarbonise supply chains (World Economic Forum, 2009, p.6): 1. Understand the carbon impact of production locations and raw materials origins optimising geographical locations in relation to raw material supplies, consumers, manufacturing plant, available energy supplies and available transport networks. 2. Reduce speed requirements review lead times to allow mode switches and transport speed reductions. The requirement for express delivery in an instant society can significantly influence the embodied energy and carbon of a product. 3. Reduce packaging use reduce transit and consumer good packaging. Bundling deliveries appropriately can cut down on both individual transport requirements and packaging. 4. Increase use of recycling and reverse logistics increase the share of end consumer goods which are recycled to encourage closed loop supply chains. This can be significantly improved within the construction industry, but relies on organisations pooling expertise and resources. 5. Revisit distribution channels increase home delivery where applicable to reduce individual shopping trips. This is less applicable to the construction industry, but the ethos of reducing journey times and frequency is critical. These five opportunities combine to give a complimentary message: sustainable supply chains are ones in which responsibility is taken from the cradle to the grave, or back to the cradle. That means that locally sourced materials, which have minimal carbon associated with their manufacture, which are durable over decades of use and which can be recycled or reused with minimal end of life processing. 3. LCA methodologies There are a number of recognised LCA approaches / LCA methodologies. These include process analysis, input output analysis and hybrid analyses. There are also simplistic / alternative approaches. These LCA approaches are briefly summarised in Figure 4 and described in more detail below. Page 16
Figure 4 LCA methodologies 3.1 Process analysis Process life cycle analysis (P LCA) is the oldest and still most commonly used method, involving the evaluation of direct and indirect energy inputs to each product stage. It usually begins with the final product and works backwards to the point of raw material extraction. The main disadvantages centre on the difficulties in obtaining data, not understanding the full process thoroughly, and extreme time and labour intensity. These result in compromises to system boundary selections (which are generally drawn around the inputs where data is available). Furthermore, it is likely to ignore some of the processes, such as services (banking and insurance, finance), inputs of small items, and ancillary activities (administration, storage). The magnitude of the incompleteness varies with the type of product or process and the depth of the study, but can be 50% or more (Lenzen et al., 2002). For these reasons, results are found to be consistently lower than the findings of other methodologies. P LCA is better used to assess or compare specific options within one particular sector. 3.2 Input output analysis Originally developed as a technique to represent financial interactions between the industries of a nation, the input output life cycle analysis (I/O LCA) can be used in inventory analysis to overcome the limitations of process analysis. This method is based on tables which represent monetary flows between sectors and can be transformed to physical flows to capture environmental fluxes between economic sectors. The number of sectors and their definition vary within each country. The great advantage of this method is data Page 17
completeness of system boundaries: the entire economic activities of a nation are represented. However, despite the comprehensive framework and complete data analysis, I/O LCA is subject to many uncertainties, due mainly to the high level of aggregation of products. Many dissimilar commodities, or sectors containing much dissimilarity, are put into the same category and assumed identical; assumptions are based on proportionality between monetary and physical flows. In some countries I/O tables are not updated frequently, resulting in temporal differences with irrelevant or unrepresentative data. Unsurprisingly, P LCA and I/O LCA yield considerably different results. I/O LCA is suitable for strategic policy making decisions (comparing sectors) as well as providing complementary data on sectors not easily covered by P LCA. To assess life cycles of older buildings, I/O LCA would be impractical, as the economic input and output data for the time of construction is not, or at least not easily, available. 3.3 Hybrid analyses The disadvantages of the previous methods can be reduced if a hybrid LCA method, combining both P LCA and I/O LCA methodologies, is employed. In this model, some of the requirements are assessed by P LCA, while the remaining requirements are covered by I/O LCA. The main disadvantage of these techniques is the risk of double counting. There are, generally speaking, four types of hybrid analysis: Process based hybrid analysis This method uses process analysis as the starting point and escapes the excessive amount of time needed to acquire the last few percent of the total, but is criticized for lacking transparency. Input/output based hybrid approach This method uses conventional I/O analysis data as the starting point. Single or groups of data in the I/O matrices are substituted with process analysis data. Tiered hybrid method Process analysis is employed for use and disposal phases as well as for several important upstream processes; the remaining input data is taken from an I/O based LCI. Aside from the risk of double counting, the interaction between the two methodologies can be difficult to assess in a systematic way. Integrated hybrid analysis Process analysis and I/O analysis are developed independently and then systematically merged into one system to form a computational structure and a consistent mathematical framework. 3.4 Simplistic / alternative approaches Due to the complexities of LCA and the complications in LCI studies, a number of simplistic methods were developed for industrial use, mainly aiming to develop quick decision making Page 18
tools. Researchers have introduced a hotspot approach, which selects essential issues in the inventory and applies generic data to quickly analyse products. This has been developed into a method of screening and streamlining to restrict LCA scope: data is obtained from a number of sources to identify environmental hotspots. These hotspots are then subject to further and fuller analysis. 3.5 Which LCA methodology should be use? The most commonly used methodologies for building components and whole new buildings are P LCA, I/O LCA and hybrid approaches. In practice it is usual to find a truncated P LCA approach, whereby the most energy intensive components and processes are captured (e.g. structure, envelope, windows, fit out) while smaller, less energy intensive components are ignored (e.g. certain fittings, signage and ironmongery). I/O LCA approaches will, by nature of the methodology, be more inclusive, but run the risk of double counting and data quality issues. Hybrid approaches, which capture much of the building through P LCA and use I/O LCA to fill in the gaps, have also been used (Treloar et al., 2000b). It is not possible to use I/O LCA to assess the embodied energy of existing buildings, as I/O data tables are not available for the period in which these buildings were constructed. Upgrades to existing buildings are, normally, most appropriately assessed using P LCA methodologies. 4. Importance on LCA base data Executing an accurate LCA relies heavily on life cycle data and inventory studies. These may include methodology assessments and database searches, in addition to direct measurements, surveys, questionnaires and possible analysis of historic data. Occasionally, theoretical calculations and personal interviews are required in addition to a clearly defined set of assumptions. Therefore, the following equation becomes clear: Independent of any tool or methodology used, Quality of LCA results = Quality of LCI data 4.1 Databases and inventories A number of databases and inventories exist to supply data for life cycle purposes. Availability of reliable data in LCA studies relates directly to the time, cost and quality of a study s output. Sources of data include academic, industrial, governmental and institutional documents; trade association reports and databases; national databases, such as statistical, economic or environmental inventories; other publicly available databases; consultancies; papers and books; and best engineering judgements. A number of these sources focus specifically on building materials and construction: for example, BRE s Environmental Profiles building materials database (BRE, 2011) and their Green Guide to Specification (Anderson et al., 2009); the US National Renewable Energy Laboratory s U.S. Life Cycle Page 19
Inventory Database for commonly used materials, products and processes; and the Canadian Athena Sustainable Materials Institute s Building Material Life Cycle Inventory Database. There is much internationally recognised, published work by academics (for example, Lenzen et al. [2000], Buchanan et al. [1994], Alcorn et al., [1998], Treloar et al., [2000a]), much of which needs updated to represent current technology, transportation and means of energy supply. The LCA methodologies consists, generally, of four distinct, analytical steps: defining the goal and scope creating the inventory assessing the impact interpreting the results These steps are described in a series of international standards, published by the International Standards Organisation (ISO), which include: ISO 14040:2006 Environmental management Life cycle assessment Principles and framework ISO 14041:1998 Environmental management Life cycle assessment Goal definition and inventory analysis ISO 14042:2000 Environmental management Life cycle assessment Life cycle impact assessment ISO 14043 :2000 Environmental management Life cycle assessment Life cycle interpretation Despite these standards, large differences between data sources exist and result in significant variation among published LCI studies. For example, the ICE database (Hammond et al., 2011) reports variation in the embodied energy of a brick between 1.5 and 13.8 MJ. Data variation is a fundamental problem in LCA studies. The most common causes include differences in scoping and boundary definitions, variations in assumptions made, and the various methodologies chosen for analysing LCIs. The Inventory of Carbon and Energy (ICE) The Inventory of Carbon and Energy (ICE), developed by Hammond and Jones (2011) at the University of Bath, is a comprehensive, but not exhaustive, database of materials which references a wide number of worldwide academic and industrial sources. A range of embodied energy, embodied carbon and equivalent carbon values are presented for various construction and other materials. Some information on study boundaries is offered, i.e. Cradle to Gate, Cradle to Site and Cradle to Grave analysis, and an estimation of the data s sensitivity is offered (typically ranging between 25% and 40%). ICE is not intended for specific construction life cycle analysis, but does contain many individual material Page 20
properties. This type of database offers useful data for the analyst wishing to perform a process based LCA study. The Blackbook The Hutchins UK Building Blackbook (Anon, 2010) is similar in style to BRE s Green Guide in that materials are listed as building components. There is no breakdown of individual materials and sources. Whereas the Green Guide adheres to LCA practices and has a defined methodology, the Blackbook seems rather less transparent in its approach, but does present absolute values, rather than an abstract rating. As with the Green Guide, the Blackbook is only useful when considering new materials for prospective projects and upgrades; it cannot be applied to older existing buildings due to a lack of data about many of the building materials used in the past. 4.2 Boundary definitions The accuracy of energy calculations is directly related to, and profoundly influenced by, boundary definitions. Naturally, more comprehensive boundary assumptions result in more precise calculations. The direct energy requirement for manufacturing processes is generally less than 50% of the total embodied energy of a product, but can be up to 80%, while the indirect energy requirement for extracting raw materials is generally less than 40% and the energy needed to make the capital equipment less than 10%. In general, the energy requirement to make the machines that make the capital equipment is very low. Inclusion / exclusion of indirect processes like raw material extraction, embodied energy of manufacturing machinery, transportation, reoccurring embodied energy of materials or the feasibility of recycling and reuse can have a significant effect on overall results. 4.3 Completeness of study The more processes are included in a study, the more complete and accurate the results become. Indirect energy contributions depend upon many factors, including raw material sources. The ICE database commonly reports data sensitivities of 30% due to varying boundary inclusions and completeness of studies (Hammond et al., 2011). 4.4 Energy supply assumptions These assumptions can produce significant variations in embodied energy evaluations, whether primary or secondary (delivered or end use). Coefficients of primary to delivered energy conversion ratios should be clarified, in addition to losses due to refining and distribution, and efficiency of energy production. If primary energy is reported instead of delivered or end use energy, the value may be 30 to 40% higher for common building materials. Lack of information regarding these factors is one of the main obstacles in comparing LCI results. Page 21